1. Field of the Invention
The present invention relates to tire information transmitters which are mounted to vehicles having wheel assemblies, such as trucks, buses, passenger cars and motor-bikes, and transmit ambient information in a tire cavity region, such as, a tire inflation pressure and a tire temperature, and the present invention also relates to tire information acquisition systems using the tire information transmitter. Priority is claimed from JP 2005-37874, the disclosure of which is incorporated herein by reference thereto.
2. Description of the Prior Art
Nowadays there have been proposed tire monitoring systems used in vehicles such as trucks, buses, passenger cars and motor-bikes, that are provided with wheel assemblies each including a wheel and a tire, for constantly monitoring a pressure (hereinafter alternatively referred to as the tire inflation pressure) in the tire cavity region surrounded by a tire internal surface and a wheel wall surface and a temperature (hereinafter alternatively referred to as the tire internal temperature) in the tire cavity region, so that an alert indicating abnormal situation is issued if the tire inflation pressure or the tire internal temperature exceeds a predetermined range.
Generally, in conventional tire information systems, a tire information transmitter is provided in the tire cavity region so as to acquire ambient information in the region and wirelessly transmit the ambient information to outside the tire cavity region.
In the conventional tire monitoring systems, the ambient information is received by a receiver provided in the vicinity of a tire house of the vehicle body, and based on the received ambient information, the presence of any abnormality is determined, so that the driver is alerted to any abnormal situation.
In the tire information transmitter of such conventional tire monitoring systems, the transmission of the ambient information is triggered by radio wave supplied from outside. Alternatively, the transmission of the ambient information is triggered by other known methods including: providing a switching device for switching; providing a lead terminal on the tire information transmitter and short-circuiting using the lead terminal; and applying a predetermined voltage to a lead terminal.
There are still other methods as will be described below that have been proposed for triggering the transmission of signals from the tire information transmitter to outside.
PATENT DOCUMENT 1 ((JP 2000-62419 A) discloses a tire air pressure detection transmitter that measures pressure using a pressure sensor and transmits the data on a predetermined period basis. The tire air pressure detection transmitter according to PATENT DOCUMENT 1 operates in a low power consumption mode until the next measuring cycle starts, if the difference between the pressure data measured in the previous measuring cycle and the pressure data measured in the current measuring cycle is not larger than a predetermined pressure difference value, in order to minimize battery power consumption. Accordingly, the tire air pressure detection transmitter of PATENT DOCUMENT 1 transmits pressure data only when the pressure difference exceeds the predetermined value. This contributes to a longer battery life.
PATENT DOCUMENT 2 (JP2002-248914A) discloses a tire condition monitoring apparatus that controls a transmission circuit to transmit data showing the measured tire condition only when the data showing the latest measured tire condition changes more than a predetermined value. In this way, a transmitter of the tire condition monitoring apparatus according to PATENT DOCUMENT 2 transmits the data showing the tire condition only when the tire condition has changed more than a predetermined value. This also provides a longer battery life.
A tire pressure monitoring system disclosed in PATENT DOCUMENT 3 (JP 3,385,529 B) is driven by battery power to wirelessly transmit a monitoring signal including a tire pressure detection value detected by a sensor to a vehicle body through a transmitting section. The system has a control section that compares the detection value provided by the sensor with a predetermined value to enable the transmitting section to wirelessly transmit the monitoring signal, if the detection value exceeds the predetermined value.
In the tire pressure monitoring system of PATENT DOCUMENT 3, the wireless transmission from the transmitting section is stopped when the detection value provided by the sensor is as low as around atmospheric pressure, thereby suppressing unnecessary power consumption of the battery power.
However, in the conventional tire information transmitters, input of radio wave from outside is necessary in order to activate the transmitter, and thereby a receiving circuit is required, causing the system configuration to be complicated. This in turn increases system cost.
In addition, for the conventional tire information transmitters, input of radio wave from outside is necessary in order to trigger the transmission of ambient information, thereby requiring additional work and time.
Further, in the conventional tire information transmitters, it is necessary to provide a switching device for switching in order to trigger the transmission of ambient information, which requires additional work and time.
In conventional tire information transmitters that are provided with a lead terminal, the transmission is triggered by applying a predetermined voltage to the lead terminal, thereby also requiring additional work and time. In addition, as described above, the conventional tire information transmitters require a switching device or a lead terminal, and a circuit for triggering transmission and the like, thereby causing the system configuration to be complicated. This increases system cost.
Further, in both of the tire air pressure detection transmitter of PATENT DOCUMENT 1, and the transmitter of the tire condition monitoring apparatus of PATENT DOCUMENT 2, the operation mode is reversibly changed depending on the measured pressure value, which causes a problem in which configuration of, such as, control circuit tends to be complicated. This increases the system cost.
In the tire pressure monitoring system of PATENT DOCUMENT 3, the transmitting section starts the wireless transmission of the monitoring signal when the detected value exceeds a predetermined value after the system has been mounted on the wheel and the tire has been rimmed and filled with air. This involves a problem in which a failure of the system can only be detected after the tire has been filled with air. For example, in case that a system does not work due to manufacturing problems, operation failure, or shock during transport, in order to replace the system it is necessary to remove the tire that has already been assembled, requiring complicated processes.